1. Field of the Invention
The present invention relates to an electron beam device comprising
(a) a cathode which is at a cathode potential and in which a high-power electron beam propagating along a beam axis is generated; PA1 (b) an anode arranged behind the cathode in the direction of the beam axis, which is at an anode potential which is increased compared with the cathode potential and accelerates the electrons of the electron beam; PA1 (c) a collector arranged behind the anode in the direction of the beam axis for decelerating the electrons of the electron beam, the collector being at a collector potential which is lower than the anode potential; and PA1 (d) a feed arrangement for providing the individual potentials for the cathode, anode and the collector. PA1 (e) the collector comprises several collector stages arranged successively in the direction of the beam axis, which are in each case on a lower potential step; PA1 (f) the feed arrangement comprises a high-voltage direct-current supply which consists of a plurality of similar switching stages which are in each case constructed as switchable medium-voltage sources and the outputs of which are connected in series; and PA1 (g) the stepped potentials of the collector stages are provided by corresponding taps between the switching stages of the high-voltage direct-current supply. PA1 (a) each of the switching stages comprises the secondary winding of a line transformer, a switching stage rectifier connected thereto, subsequent means for smoothing the rectified voltage and at least one switching stage switch located at the output and controlled by a stage controller; and PA1 (b) a reversely polarized cascade diode is arranged in each case between the outputs of each switching stage.
Such an electron beam device is known, for example, as a quasi-optical gyrotron with a "depressed collector" from the Article by H.-G. Mathews, J. de Physique, Colloque C1, supplement au no. 1, Tome 50, January 1989, pages C1-643 to C1-658 (in particular, see FIG. 11 in this document).
2. Discussion of Background
Feed arrangements for high-power gyrotron tubes are used, for example, for plasma heating in plasma fusion experiments (ECRH=Electron Cyclotron Resonance Heating) at present mainly operate with a system of high-tension transformer, rectifier, tube modulator and capacitor bank. To protect the gyrotron tube, a series circuit of ignitrons is also used as a "crowbar", which limits or destroys the energy stored in the system. A high-power tetrode such as that offered commercially by, for example, Asea Brown Boveri AG under the type number CQK 200-4, has been successful as switching and regulating tube.
Currently used gyrotron tubes such as, for example, the GT 92-5p type, also manufactured and offered by Asea Brown Boveri AG, operate with cathode voltages of up to -90 kV and currents of up to 50 A which must be provided by the feed arrangement. In individual cases, feed arrangements are also used which supply up to 3 gyrotron tubes at the same time.
To turn the gyrotron tube off or on, a separate low-power tube modulator is used in the prior art, which switches the auxiliary or modulation anode between 0 and approx. +30 kV with respect to the cathode potential. Gyrotron tubes without an auxiliary anode are also used, the modulation in this case being limited by the switching speed of the high-power cathode modulator.
To increase their efficiency, gyrotron tubes of the next generation will be equipped with a so-called "depressed collector" described in the printed document mentioned initially, the potential of which is lowered with respect to the anode and which, as an electron collector, decelerates the electrons of the high-power electron beam before it is dissipated.
A desirable feature with respect to the efficiency would be a division of the collector into several collector stages arranged successively which would in each case be on a lower potential step. However, this would require high-power high-tension feed arrangements for supplying the individual collector stages which could only be implemented at great expense by means of the high-voltage tube modulators used in the prior art.